Superregenerative magnetron receiver



. I Oct. 21, 1941. R. A. BRADEN 2,259,549

' SUPERREGENERATIVE MAGNETRON RECEIVER Original Filed' Jan. 31 1958 s 'Sheeis-Sheet 1 3 M 0 l0" d :""*L' 5 55? A, M D/6570K]:

FREQUENCY IMP. IND IND/CF70 QUE/VCH 6a O SC 3nnentor Rene H. Braden I I l D Y .l l l' I'l BB Gflorneg SUPERREGENERATIVE MAGNETRON RECEIVER R. A. BRADYEN Original Filed Jan. 31, 1938 7 -.9 BAP 101 I I I 3 Sheets-Sheet 2 MID/(670E.

MODULIV'IO/V IMP- 4ND rwzauzucr netron.

quenching voltage is applied to the end-plates;

Patented Oct. 21, 1941 UNITED STATES PATENT, oFiicE' 2,259,549 I I SUPERREGENERATIVE MAGNETRGN aecnrvna Rene A. Braden, Collingswood, N. J., assignor to Radio Corporation of America, a corporation or Delaware ()riginai application January 31, late-semi No.

187,942. Divided and this application February 29, 1940, Serial No. 321,550

8 Claims.

My invention relates to ultra short wave receivers, and more particularly to a receiver having a. superregenerative magnetron detector.

vThis application is a division of my copending application Serial No. 187,942, filed January 31, 1938, for Superregenerative magnetron receiver granted August 13, 1940, as U. S. Patent No. 2,211,091.

The practice of superregeneration as applied to thermionic detectors operating in th usual range of radio signalling frequencies is well known. I have discovered that the conditions causing superregeneration which results in the increased sensitivity of an oscillating detector can be applied to a magnetron. Essentially these conditions are met by a detector which is capable of self-oscillation when suitable values of electrode potentials are applied and in which oscillations are interrupted by periodic variations of the electrode potentials.

It is an object of this invention to provide means for obtaining superregeneration in a mag- In its simplest form, a magnetron detector is essentially a two-electrode device. In consequence, the signal input circuit, the quench voltage circuit, and the modulation frequency output circuit are all attached to the same pair of electrodes. This results in the direct application of quench voltages to the modulation frequency amplifler. The amplifier is consequently overloaded so that it does not effectively amplify the demodulated signal.

It is therefore a further object of my invention to provide means for protecting the modulation frequency amplifier of a superregenerative magnetron detector from being overloaded by the quench frequency oscillations.

Another object is to provide means for generating quenching voltages in a magnetron oscillator.

A further object is to provide means for applying quenching voltages to magnetrons having auxiliary electrodes.

My invention will be better understood from the following description when considered in connection with the accompanying drawings. Its scope is indicated by the appended claims.

Referring to the drawings,

Figure 1 is acircuit diagram of a magnetron detector in which a negative resistance characteristic of a magnetron is used to provide seli"-ex-' cited quench oscillations;

Z'represents a superregenerative endplate magnetron detector in which an in-phase Figure 3 is the same as Fig; 2 except that an out-of-phase quenching voltage is applied to the end-plates;

- Figure 4 is another circuit for quenching an 5 end-plate magnetron detector and for protecting the modulation frequency amplifier from the quench frequency voltages.

Figure 5 is a schematic diagram of a selfexcited end-plate magnetron detector, in which the end-plates are used to obtain feedback for generating quench frequency :voltages; Figure 6 is a schematic diagram of a double end-plate magnetron in which the end-plates constitute the quench frequency oscillating electrodes;

Figure 7 is a schematic diagram of an alternative type of magnetron detector in which a second emissive cathode and a grid provide regenerative feedback to the anodes for the generation of quench frequency oscillations;

Figure 8 is a schematic diagram of a ,split anode magnetron detector in which quench frequency oscillations are generated in auxiliary electrodes.

Q Similar numerals refer to' similar parts throughout the several drawings.

Referring to Fig. 1, a. split anode magnetron tube is shown at I having anodes 3 and 5, emissive cathode 'I heated bya battery 9, one terminal of 0. which is grounded. A magnetic field parallel to the cathode is indicated .by the pole pieces 2 and 4 of a magnet which is not shown. A tunable transmission line H, l3 connects the anodes to a dipole antenna i5. Tuning is accomplished 5 byvarying the length of II and I3. The midpoint of the antenna is serially connected to the positive terminal of a potential source, such as battery 3|, through a choke coil I I, a tuned cir-, cuit 5| and a resistor I9. The battery. 3| has its 40 negative terminal grounded, and may be bypassed by a capacitor 2|.

Ultra short wave signals are received on the antenna l5, and fed to the magnetron anodes through the transmission line. A voltage corre- 4-5 sponding to the modulation of the received signal The quench voltage is usually comparatively high. Should it be impressed directly across the amplifier, the grid of the first amplifier tube would be driven positive during a portionof the cycle, and below negative cut-'ofi during a portion 5; of the cycle. Thiswould cause distortion,- a reduction of gain, or plifler. The purpose of the filter 33 is to prevent 'the'quench frequency voltage from reaching the amplifier 29. The filter may be designed in the usual manner to provide low pass characteristics for audio mpdulations, or band pass characteristics for high frequency modulations. In either case it should present a high degree of attenuation to the quench frequency voltage.

Self-generated quench oscillations are produced in the anode circuit of the tube. A shunt resonant circuit comprising an inductor 53 and a capacitor 55. is inserted in the anode lead to the magnetron between resistor I9 and choke II. By virtue of the negative resistance'characteristic of the magnetron, quenching oscillations are generated whose frequency is determined by the resonant frequency of the resonant circuit 5|. These quenching oscillations occur simultaneously with the ultra short wave oscillations and, as a result, the anode potential is varied, interrupting the latter oscillations at the-frequency of the former. Increased sensitivity'due to the superregenerative action results.

Fig. 2 illustrates an embodiment of my invention in which the quenchingvoltage is applied to the end plates of an end-plate magnetron 39. Two anode sections II and 13 are connected to the antenna I5 through the transmission line H, I3. The mid-point of the antenna is connected to the positive terminal of the anode voltage supply through choke IT and resistor I9. The demodulated output is taken from the juncquench frequencies.

complete blocking of the amsible; for example, the quench voltage may be applied to the anode, and the demodulated signal taken from the end plates, as shown in Fig. 4. This capacitor presents negligible impedance to signal frequencies, but a high impedance to Two choke coils 24 and 26 are provided through which the out-of-phase quench voltage is applied to anodes II and 13 from the secondary 99. A voltage of twice the quench frequency appears across resistor I9 as in Fig. 3, and similarly may be attenuated by a filter 30.

Other combinations which maybe employed include applying the quenching voltage simultaneously in opposite phase to the two end plates, and to the two split anodes inproper magnitude and phase to effect a balance with respect to the total current to the split anodes. Or the signal may be appliedto either pair of electrodes inphase, andthe detected signal taken out of remaining pair, in phase.

Figure 5 is a schematic diagram of another method of obtaining superregenerative detection with an end plate magnetron. A regenerative feedback coupling to the end plates I95 and I3! the has been provided which includes the mutual tion of choke I1 and resistor I9 through capaci-'- tor 21. The two end plates 15 and TI are connected together by leads 93 and to the positive terminal of a battery 9| through a choke 8| and the secondary 33 of, a transformer 95. The

quenching voltage is then induced in series with the fixed potential from 9| by the oscillator 89 and transformer 95. Since an increase in enda plate potential causes an increase in end-platecurrent and a decrease in anode current, and vice versa, the quenching frequency may also appearin the modulation frequency amplifier. Precautions must be taken to prevent this. The use of a suitable filter has been explained in the parent application referred to above.

Fig. 3 shows a method of protecting the modulation frequency amplifier from the quench voltage which has particular application to an endplate magnetron. Except for the end-plate connections, the usual magnetron circuit is shown. The quenching voltage from the oscillator 89 is applied through a push-pull transformer 91 out of phase to the two end plates 15 and TI. The mid-point of the secondary 99 of this transformer is connected through a choke I03 to the positive terminal of the source of end-plate potential 9|. Consequently, at any instant the modulating effect of one plate on the anode current is parcoupling between inductor 53, which is in the anode circuit, and inductor III, which is connected between the end plates and the end-plate battery 9|. One, or both, of these inductors may be tuned by a variable capacitor. When the magnetic coupling between inductor III and inductor 53 is properly phased, quenching oscillations will be generated at a frequency which is determined by the resonant frequency of one,

.or both, of the tuned circuits. As before, the

variation of anode potential interrupts the ultra short wave oscillations at the quench frequency, and superregenerative detection results.

In Fig. 6 is shown a superregenerative magnetron detector circuit which employs a magnetron ||3 having an additional electrode associated with each end plate which is preferably an annular electrode 5. The end-plate battery 9| supplies a positive potential to both end plates II'I through an inductor 9. A battery I23 supplies a negative potential to the electrodes III through an inductor |2| inductively coupled to 1 9. One or both of these inductors may be tuned, as by capacitors I19 and I29. Quench I oscillations are generated between these electially cancelled by the equal and opposite effect separate more efiiciently the desired slgnal'from the undesired when the difference between them is great.

I have found that other combinations are postrodes at the resonant frequency of one, or both, of the tuned circuits. The varying-potential on the end plates I I1 interrupts the signal frequency oscillations of the magnetron toproduce superregeneration. While the annular electrodes II! have been shown concentric to and in the P ane of the end plates they are not limtied to that position, nor indeed are they to be limited to the annular shape illustrated. They may take the form of grids and be placed, for example, between the end plates I I1 and the anodes 13.

A further variation of the method ofobtaining quenching oscillations is shown in Fig. 7. A

split anode magnetron I25 is provided with a second emissive cathode I33 and a grid |3|. The grid is negatively biased by a battery I II and coupled to the anode circuit through inductor'l 33 coupled to a shunt tuned circuit |3'I in the anode circuit.- The cathode I33, the-grid |3| and the anodes 1|, 13 function as a triode thermionic tube. Regenerative feedback at the quench frequency is produced by the proper phasing of the coupled circuits I39 and I31, and quenching oscillations are produced at a frequency detervoltages.

mined by I31. This, again, results in a variation of the anode potential which quenches the signal frequency oscillation to produce superregeneration.

Fig. 8 shows a still further variation in which two end plates I43 are added to the magnetron of Fig. 7. The resonant circuit I31 is now in serieswith the end-plate potential source 9|, and

said inductors, whereby local oscillation takes place between said end plate and said auxiliary is coupled to a grid inductor I39. The second cathode I33, grid l3! and end plates I43 perform thermionic triode functionsto generate quench frequency oscillations. The modulation frequency output is taken from the anodes in the usual manner.

I have thus shown how the sensitivity of an ultra short wave magnetron detector may be greatly increased by an application of the-principles of superregeneration, and I have shownhow the quenching oscillations may be generated by the magnetron tube itself, and I have shown various methods of protecting theaudio system from the effect of excessive quench frequency Iclaim as my invention:

1. The combination including means receptive to radio frequency signals, an osclllating'mag netron detector having a cathode, one or.more anodes, and-one or more end plates,means for impressing said signals on said magnetron anodes, and means including said end plates for interrupting said oscillations whereby superregenerative detection is established.

electrode, at a frequency determined by said resonant inductor, said local oscillation having sufficient magnitude to interrupt said radio frequency oscillations, whereby superregenerative -nal frequency oscillations thereby producing superregenerative detection in said magnetron.

5. A device of the character in claim 2 which is further characterized by means for preventing oscillations of twice said interruption frequency from being impressed on said indicating means.

6. In an ultra'short wave receiver including a magnetron detector connected to a source of en-.

ergizing potential and oscillating at signal'frev quency, the method of utilizing the-negativeresistance characteristic of said magnetron which includes the steps of generating a quench frequency potential by a shunt resonantcircuit,

serially connected between said energizing po- 2. In an ultra shortwave receiver including an.

oscillating magnetron detector having a cathode, one or more anodes and a plurality of end plates, and means associated with said anodes for indicating demodulatedsignal impulses, means for periodically interrupting saidmagnetron oscillations including a source of alternating potential of interruption frequency, and means for impressing said alternating potentials on said end plates in phase opposition whereby superregenerative detection takes place.

3. A system comprising means. receptive to modulated radio frequency signals, a magnetron device oscillating at said radio frequency having a cathode, one or more anodes, at least one end plate and at least one auxiliary electrode, means for impressing said radio frequency signals on said anodes, means for generating local oscillations having a frequency lower than said radio frequency oscillations, said means including a' first inductor associated with said end plates, a

tential source and said magnetron detector and tuned to a frequencylower than said signal fresecond inductorassociated with said auxiliary electrode magnetically coupled to said first inductor; and means for resonating at least one of quency, andinterrupting said magnetron signal frequency oscillations by said quench frequency potential to produce superregeneration. '7. The combination including means receptive to radio frequency signals, an oscillating magnetron detector having a cathode, one or more anodes, and one or more end plates, means for impressing said signals on said magnetron anodes, a source of interruption frequency oscillations, and means for varying the potential of said'end plates with respect to ground in accordance with said oscillations. 8. The combination including means receptive to radio. frequency signals, an oscillating magnetron detector having a'cathode, one or more anodes, and one or more end plates, means for impressing said signals on said magnetron anodes, a source of interruption frequency oscillations, and means for varying the potential of said end plates in phase with respect to ground in accordance. with said oscillations. RENE A.-BRADEN. 

